[Trilinos-Users] Sparse matrix and Anasazi Solvers,

[Mike Atambo]

Alicia,
I will take a look at that  try it on my problem
thanks,
Mike

On Thu, Feb 5, 2015 at 8:22 PM, Alicia Klinvex <aklinvex at purdue.edu> wrote:

> Hello Mike,
>
> I'm pretty sure your Trilinos code is NOT using shift-and-invert with BKS.
>  (Shift-and-invert is the spectral transformation I described before.)  If
> you want to use shift-and-invert, you must construct the linear solver
> yourself and give it to the BKS solver manager.  Some examples of that can
> be found on this page:
> http://trilinos.org/docs/r11.12/packages/anasazi/doc/html/examples.html
>
> If you want to use a sparse factorization, then the Amesos example should
> be of interest to you.  If you want to use a preconditioned Krylov method
> to solve the linear systems that arise at each iteration of BKS, then look
> at the Belos example.  Let me know if those examples don't make sense to
> you.
>
> Best wishes,
> Alicia
>
> Disclaimer: I am an external collaborator at Sandia, and I did not write
> the BKS code.  I can help you with the mechanics of getting things to run,
> but Heidi Thornquist and Rich Lehoucq (who are also on the user mailing
> list) would probably know more about how to get good performance out of BKS
> and block Davidson.
>
> On Thu, Feb 5, 2015 at 1:50 PM, Mike Atambo <mikeat4999 at gmail.com> wrote:
>
>> Alicia,
>> Im still trying to figure  out what exactly im facing. Maybe what you
>> described be the issue, but  at this
>> point i would prefer to try out what you have suggested, if it works,
>> then it would be certain thats what im facing,
>> if not, then i can rule that out.
>> Please let me know how to  set the krylov-shur  solver   as you
>> suggested,
>> here are the parameters i pass to  the anasaziPL   for Krylov-Shur at the
>> moment:
>>
>>   const double tol = 1.0e-8;
>>   const int maxIters = 500;
>>   anasaziPL.set ("Which", "SR");
>>   anasaziPL.set ("Block Size",1 );
>>   //anasaziPL.set ("Maximum Iterations", maxIters);
>>   anasaziPL.set ("Convergence Tolerance", tol);
>>   anasaziPL.set ("Full Ortho", true);
>>   anasaziPL.set ("Use Locking", true);
>>
>> Mike.
>>
>>
>> On Thu, Feb 5, 2015 at 5:47 PM, Alicia Klinvex <aklinvex at purdue.edu>
>> wrote:
>>
>>> Hi Mike,
>>>
>>> If ARPACK is working for you and block Krylov-Schur is not, I suspect
>>> that one is using a spectral transformation and the other is not.
>>>
>>> I don't know much about scipy's eigs, but I assume it is similar to
>>> Matlab's eigs (which also uses ARPACK).  When you ask Matlab's eigs to find
>>> the smallest eigenvalues of a matrix, it will automatically transform the
>>> problem of finding the smallest eigenpairs of A x = \lambda x into the
>>> equivalent problem of finding the largest eigenpairs of A^{-1} x =
>>> \lambda^{-1}x.  Anasazi's Krylov Schur does not do that unless you
>>> explicitly tell it to.  Could that be the problem you're having?  If so, we
>>> can discuss how to tell Krylov-Schur that's what you want to do.
>>>
>>> Best wishes,
>>> Alicia Klinvex
>>>
>>> On Thu, Feb 5, 2015 at 11:21 AM, Mike Atambo <mikeat4999 at gmail.com>
>>> wrote:
>>>
>>>> Hi,
>>>> Im unable to get matrices,  ( say a sparse matrix with
>>>> 885500 non zeros  out of  about  2822796900 )   to converge
>>>> with the block davison or the krylov solver,
>>>>
>>>> I had a look at the condition number reported by the 'ILUT'
>>>> preconditioner and it seems to grow rather quickly for my  problems,  ( 9x9
>>>>  with 39 non zeros has  condition number= 10,   and at    25*25 and 100 non
>>>> zeros the condition number is at 250).
>>>>
>>>> Im able to solve all these examples here using scipy.sparse.eigs  (it
>>>> uses ARPACK),  so there is probably something that im not doing right.
>>>>
>>>> The block-davidson solver with 'ILUT' pre-conditioner   work for the
>>>> small systems above,   but  beyond  300*300 matrix size,  this is not
>>>> longer true.
>>>>
>>>> At the moment im  following these steps.
>>>>
>>>> 1.  Create and initialize a matrix,
>>>> 2.  Create an anasazi basic eigenproblem,
>>>> 3.  Create a  solver (either block davidson or krylov-shur)
>>>> 4.   Get solution,
>>>>
>>>> Id like to find out whether there is a way to tell why the system  im
>>>> working on seems
>>>> to be  unable to converge.  Any help would be appreciated.
>>>>
>>>> Mike
>>>>
>>>>
>>>> --
>>>> M. O. Atambo
>>>> mikeat4999 at gmail.com
>>>> matambo at ictp.it
>>>> Ext .139
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> Trilinos-Users mailing list
>>>> Trilinos-Users at software.sandia.gov
>>>> https://software.sandia.gov/mailman/listinfo/trilinos-users
>>>>
>>>>
>>>
>>
>>
>> --
>> M. O. Atambo
>> mikeat4999 at gmail.com
>> matambo at ictp.it
>> Ext .139
>> Room 209.
>>
>>
>


-- 
M. O. Atambo
mikeat4999 at gmail.com
matambo at ictp.it
Ext .139
Room 209.
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